In a plasma processing apparatus used in a semiconductor device manufacturing process, a substrate to be processed such as a semiconductor wafer or the like is mounted on a substrate mounting table provided in a processing chamber, and a high frequency voltage is applied to the processing chamber under a vacuum environment. Accordingly, a plasma is generated in the processing chamber, and, e.g., etching of the substrate is carried out. In such a plasma processing apparatus, a focus ring is provided at an outer peripheral portion of the substrate mounted on the mounting table to improve in-plane uniformity of the plasma processing of the substrate.
In the above configuration, it is general that a vacuum insulating layer is formed between the focus ring and a top surface of the outer peripheral portion of the mounting table in the depressurized processing chamber and, thus, thermal conductivity between the focus ring and the top surface of the outer peripheral portion of the mounting table becomes considerably poor. When the vacuum insulating layer is formed, it is difficult to cool the focus ring, so that the temperature of the focus ring is increased. As a result, an etching rate and a hole forming property (in which a hole can be reliably formed to a predetermined depth by etching) of the outer peripheral portion of the semiconductor wafer which is close to the focus ring become poorer, and an etching aspect ratio become smaller. In other words, the etching characteristics of the outer peripheral portion of the semiconductor wafer become poorer.
If the plasma processing is continued in the above state, heat is accumulated at the focus ring and, thus, the temperature of the focus ring is not maintained at a constant level. Accordingly, it is difficult to perform uniform etching on a plurality of semiconductor wafers in a same lot.
In order to effectively cool the focus ring, a thermally conductive sheet having good thermal conductivity is inserted between the focus ring and the top surface of the outer peripheral portion of the mounting table. In the case of attaching the thermally conductive sheet, existence of even an extremely small amount of air between the focus ring and the thermally conductive sheet or between the thermally conductive sheet and the portion above the outer peripheral portion of the mounting table leads to insufficient thermal conductivity and insufficient cooling of the focus ring. To that end, an operation of improving the adhesivity of the thermally conductive sheet by repetitively increasing and decreasing a pressure in the chamber or by applying a load by a mechanical pressing unit is carried out when the thermally conductive sheet is attached.
In the plasma processing apparatus including the focus ring, the focus ring is exposed to the plasma and thus is consumed by the etching. As the focus ring is consumed, the in-plane uniformity in the processing of the semiconductor wafer becomes poorer. Therefore, when the focus ring is consumed to a certain extent, the consumed focus ring needs to be exchanged with a new focus ring. However, when the consumed focus ring is detached for exchange from the top surface of the outer peripheral portion of the mounting table, the thermally conductive sheet firmly adhered by the mechanical pressing unit may be broken.